1. Field of the Invention
The present invention relates to an in-mold foam molding apparatus and method suitable for molding into a unitary molding molded portions comprising bead starting materials having different properties, and to in-mold foam molded articles.
2. Description of the Related Art
An in-mold foam molding apparatus for fabricating moldings from bead starting materials consisting of thermoplastic synthetic resin is taught, for example, in U.S. Pat. No. 5,164,257, which discloses an in-mold foam molding technique wherein the mold is provided with moveable partitioning members that are retractable from the mold cavity via actuators such as air cylinders, the mold cavity being partitioned into a plurality of partitioned mold chambers by means of these moveable partitioning members, with filling devices for supplying bead starting materials to the individual partitioned mold chambers being connected therewith individually, whereby with the mold cavity partitioned by the moveable partitioning members, adjacent partitioned mold chambers can be filled with bead starting materials having, for example, different degrees of expansion, and once so filled the moveable partitioning members can be retracted and steam supplied to the interior of the mold cavity in order to heat and weld the bead starting materials into a molded article.
In molded articles molded by means of this in-mold foam molding technique, by varying the bead starting materials used for different regions of a molded article it is possible to fabricate a molded article having, for example, different mechanical properties in different regions thereof. This has the advantage of being able to improve functionality and quality in molded articles, which are used as cores for car bumpers and cushioning materials for packaging of household electronics, furniture, and the like.
In the in-mold foam molding apparatus disclosed in the cited U.S. publication, it is necessary to provide actuators for retracting the partitioning members, and thus a larger number of partitioned mold chambers will require a correspondingly complicated drive system for the partitioning members, resulting in the problem of higher fabrication costs for the in-mold foam molding apparatus.
Further, if filling compression in adjacent partitioned mold chambers is not controlled in such a way as prevent pressure differentials from forming, there is a risk of a partitioning member deforming due to the pressure differential. Another problem is that the flow of air used for filling is obstructed by the partitioning members, depressing ease with which the mold may be filled with the bead starting materials.
In this in-mold foam molding apparatus, since passage orifices are formed in the mold so that the partitioning members may be retracted through these passage orifices, there is the additional problem that flash forms on the surface of the molded article around these passage orifices for the following two reasons.
(1) Reason 1
In order to prevent the bead starting materials from infiltrating, the wall of the passage orifice and the partitioning member will ideally be designed with as narrow a gap as possible therebetween, but this arrangement creates the problem of deformation or breakage of a partitioning member or inability to retract a partitioning member due to contact with the inside wall of a passage orifice resulting from expansion or contraction of the mold. Specifically, the mold expands when the bead starting materials are steam heated and contracts during cooling with cooling water. Where passage orifices like those described earlier are provided, mold strength is lower in the portions bordering the passage orifices, so strain in the mold becomes concentrated at the passage orifices, and is compensated for by expansion and contraction of the width of the apertures of the passage orifices. Where the passage orifices are of xe2x80x9cLxe2x80x9d or xe2x80x9cCxe2x80x9d configuration, lower mold strength in a specific direction will result in shape deformation of passage orifices. Expansion/contraction or deformation of passage orifices may result in deformation or breakage of a partitioning member through contact with the inside wall of a passage orifice. Where the mold is split into a plurality of molding sections by the passage orifices with the plurality of molding sections being fixed by means of screws or the like to an attachment plate, it will be a simple matter to form passage orifices in the mold, but expansion or contraction of the mold will result in shifting of the locations at which the mold segments are attached to the attachment plate, so that there will be significant deviation in the width of the passage orifice apertures. This phenomenon becomes more pronounced with larger mold dimensions or longer passage orifices, and represents a significant problem for in-mold foam molding apparatuses equipped with partitioning members. For such reasons, the partitioning member and the wall of the passage orifice are designed with a large gap therebetween, notwithstanding the fact that it is recognized that flash will form on the surface of the molded article around the passage orifices.
(2) Reason 2
Partitioning member distal edge shape is designed to conform to the shape of the inside surface of the mold, but as shape is not always the same as that of the inside surface of a mold provided with passage orifices, it may occur that when a partitioning member is retracted after filling the mold with bead starting materials, the partitioning member recesses partway into its passage orifice so that th e interior of the passage orifice communicates with the mold cavity. Since the width of the passage orifice apertures is designed to be smaller than the diameter of the bead starting materials in order to prevent bead starting materials from infiltrating into passage orifices, merely retracting the partitioning members will not result i n bead starting materials infiltrating into passage orifices, but when the bead starting materials are heated and welded by delivering steam to the mold cavity, softening and expansion of the bead starting materials may result in partial infiltration into passage orifices, producing long, thin flash projecting out at locations on the molded article corresponding to the locations of passage orifices.
Flash is not a particular problem for molded articles of which only rough dimensional accuracy on the surface is required, but represents a product defect for molded articles subject to strict requirements. For example, in car bumpers, it is common practice to affix an in-mold foam molded core to the front face of front beam of the car, and to then arrange a synthetic resin cover member so as to cover the core. With car bumpers of this type, flash must be removed from the core after molding in order to prevent problems such as inability to secure the core to the proper location on the mounting face of the front beam or inability to secure the cover member at the proper location on the vehicle body due to the presence of a gap between core and front beam or core and cover member.
Japanese Unexamined Patent Application H10-193375 discloses a molding apparatus for molding foam molded articles that have molded sections consisting of bead starting materials of different properties and that can be used as shock absorbent materials, the apparatus provided with fixed partitioning members situated at the boundaries of adjacent partitioned mold chambers, with these partitioning members defining spaces wherein the bead starting materials are fused. This molding apparatus is designed such that slits are formed in the molded article by the partitioning members, whereby the molded article can be split at the slits into smaller pieces by hand, thereby facilitating disposal or recycling of the molded article after use. However, the design of the molding apparatus disclosed in this publication is provided with these partitioning members situated along certain portions of the boundaries between adjacent partitioned mold chambers, in order to form slits in the molded article, and while the specifics of the partitioning arrangement for the other portions of the boundaries is not disclosed, it may be surmised that partitioning thereof is accomplished by means of partitioning members that are retractable from the mold, since fusion of the bead starting materials overall can be visually confirmed.
An in-mold foam molding apparatus of typical configuration for producing molded article from bead starting materials comprising thermoplastic synthetic resin is depicted in FIG. 35, wherein a set of opposing molds 200, 201 is provided, the two molds 200, 201 having chambers 202, 203 formed on their respective back faces and the two molds 200, 201 having respectively formed therein a multitude of air orifices 205, 206 whereby chambers 202, 203 communicate with a mold cavity 204 so that a service fluid, such as steam, may be delivered to molding cavity 204 via air orifices 205, 206 or vented from molding cavity 204. In this example, respective chambers 202, 203 are provided in the top portions thereof with top service orifices 207, 208 for delivering as heating steam or the like, and in the bottom portions thereof with bottom service orifices 209, 210 connecting to a vacuum pump or drain pipe so that steam may delivered to molding cavity 204.
In actual practice, as shown in FIGS. 36 and 37, the multitude of air orifices 205, 206 extending through molds 200, 201 are composed of core vents 211xe2x80x94capped tubular elements having an outside diameter of 7-12 mm and perforated by a plurality of air orifices 205, 206 comprising round orifices about 0.5 mm in diameter or slits about 0.5 mm widexe2x80x94which fit within core vent mounting orifices 212 provided to molds 200, 201; and core vent holes 213 about 0.5 mm in diameter formed directly in molds 200, 201. Air orifices 205, 206 are arranged at 20-50 mm pitch on molds 200, 201.
In an in-mold foam molding apparatus of this kind, pre-expanded bead starting materials are packed into mold cavity 204, heated with steam to bring about expansion and fusion thereof, and then cooled and hardened to give a foam molded article of the desired configuration. The function of air orifices 205, 206 during foam molding is discussed further.
Japanese Unexamined Patent Application S57-174223 discloses a process diagram like that shown in FIG. 38 wherein (a) to (e) depict a preheating/evacuation process for replacing air in the mold and air between bead starting materials with steam, the specifics being described hereinbelow. In the drawing, solid black valve symbols indicate the closed state and white valve symbols indicate the open state.
(a) is an evacuation step wherein once the bead starting materials have been packed into the mold cavity 204 steam is delivered for a very brief period to chambers 202, 203 via top service orifices 207, 208, and air in the mold interior, and particularly in chambers 202, 203, is suctioned and evacuated therefrom via bottom service orifices 209, 210 to evacuate the interior. Here, chambers 202, 203 are brought to positive pressure by the steam, and steam penetrates between the bead starting materials via air orifices 205, 206.
(b) is a two-end evacuation step wherein top service orifices 207, 208 are closed while continuing the suction evacuation procedure to lower the pressure within the mold, whereby any air present between the bead starting materials is suctioned and evacuated via air orifices 205, 206 provided to both ends of the mold.
(c) is a one-sided preheating step wherein bottom service orifices 209, 210 are closed and steam is delivered for a brief period via the top service orifice 208 of one of the depressurized chambers 203. The supplied steam flows from air orifice 206 of mold 201, through the bead starting materials in mold cavity 204, and through air orifice 205 of mold 200 to reach chamber 202 on the opposite side, thereby heating the bead starting materials and all areas of molds 200, 201.
(d) is a one-sided preheating step wherein the direction of steam flow is reversed, wherein an analogous procedure is conducted, but from the chamber 202 side, whereby air present within mold cavity 204 is completely expelled and preheating is conducted while minimizing localized temperature differentials between the two molds 200, 201.
(e) is a fusing/heating step wherein steam for fusing/heating is supplied to both chambers 202, 203, thereby heating the molds 200, 201 and also heating the bead starting materials via the air orifices 205, 206 of the respective molds 200, 201 in order to complete expansion and fuse the beads together to produce a foam molded article.
The air orifices 205, 206 provided to molds 200, 201 function as passages for evacuating air present between the bead starting materials and as passages for delivering steam, and as such serve an important function in terms of producing a homogeneous foam molded article. On the other hand, the following problems have been noted.
(1) To compensate for lower mold strength resulting from the mold being perforated by a multitude of air orifices, mold wall thickness in molds consisting of aluminum alloys must be on the order of 8-12 mm, for example. However, this has the effect of increasing the heat capacity of the mold, lowering heat efficiency during heating/cooling so that the rate of temperature rise and temperature drop are slower, reducing the precision of control.
(2) Typically, a pair of molds is provided with some 2000 to 4000 air orifices, so the process of making the orifices is complicated and results in higher fabrication costs. Since the core vents are installed by hand in mounting orifices provided in the mold, the operation is quite complicated and damage to mold surfaces is unavoidable, thus requiring retouching.
(3) Since clogging of air orifices (core vents, core vent holes, etc.) by scale or the like can result in heating defects, mold release defects, or cooling defects, the core vents must be replaced or periodically subjected to high pressure washing or other maintenance procedure.
(4) Since air orifices leave marks on foam molded article surfaces, the visual appeal of molded articles suffers, and when the exterior surface is subjected to printing or the like, air orifice marks may impair printing.
(5) Since the foam molded article is cooled by spraying cooling water into the chamber after molding, water infiltrates into the molding cavity through the air orifices, resulting in water content of about 6-10% in the molded article, necessitating a drying process. Further, since cooling water comes into direct contact with the molded article, pure cooling water must be used in order to produce sanitary molded articles.
(6) As steam is passed from the chamber into the mold cavity to heat the bead starting materials under the same heating conditions in order to effect expansion/fusion thereof, molded articles produced in this way (hereinbelow referred to as isothermal molded articles) develop varying surface qualities depending upon the extent of fusion of the beads. Specifically, lower fusion rates are associated with poor surface qualities, whereas higher fusion rates associated with good surface qualities. For isothermal molded articles, higher bead fusion rates improve physical properties such as the mechanical strength of the molded article, but require longer heating, expansion/fusion times and cooling times, creating the problem of longer molding cycle times overall and reduced throughput.
For such reasons, in the molding technique described earlier, bead fusion rates are typically set to 40%-80%, for example, in order to assure good surface qualities and attractive appearance as well as assuring a fusion rate adequate to assure mechanical strength. However, even where mechanical strength requirements for a molded article are not particularly stringent, the need to assure an attractive appearance requires a moderately high fusion rate, which will result in a correspondingly longer molding cycle time and reduced throughput. Fusion rate as used herein is ascertained by splitting the molded article and observing the condition of the beads on the sectional face, specifically, by measuring the proportion of beads experiencing breakdown of the bead per se, deeming beads having cracking along the bead surface but without bursting of the bead per se to be unfused and deeming beads experiencing bursting of the bead per se into fragments to be fused.
The foam molding process described hereinabove is designed such that air orifices such as core vents and core vent holes are used to deliver steam, air, or other service fluids to the mold cavity or to evacuate same from the mold cavity during production of foam molded articles. However, as noted, the provision of air orifices creates number of problems.
With the goal of providing a fundamental solution to these problems, the inventors conducted extensive research concerning development of a foam molding process employing molds devoid of air orifices, and conducted tests of various kinds. While the goal is a mold xe2x80x9cdevoid of air orifices,xe2x80x9d it is of course necessary to provide, in lieu of core vents and core vent holes, passages for delivering/evacuating steam, air, or other service fluids to and from the mold cavity, which gives rise to the issue of where and how to form same, of the timing and conditions that should be employed in delivering service fluids to such passages, and a host of other issues that need to be addressed.
It is an object of invention to provide: a significantly simplified design for a molding apparatus capable of molding into a unitary molding molded portions comprising bead starting materials having different properties; an in-mold foam molding apparatus and method that obviate the various difficulties associated with the use of partitioning members; and an in-mold foam molded article devoid of flash protruding outwardly from the visible surfaces thereof.
The in-mold foam molding apparatus which pertains to the present invention comprises: a plurality of partitioning members for dividing into a plurality of partitioned mold chambers a mold cavity defined by a core mold and a cavity mold, at least some of the plurality of partitioned molding sections constituting the partitioned mold chambers within the mold being unitary; and filling devices for filling the partitioned mold chambers with bead starting materials, whereby adjacent partitioned mold chambers can be filled with bead starting materials having different properties.
In this in-mold foam molding apparatus, with the mold cavity partitioned into a plurality of partitioned mold chambers by partitioning members, adjacent partitioned mold chambers can be filled with bead starting materials having different properties, allowing the functionality and quality of molded articles to be improved through appropriate selection of partitioned mold chamber molding location and size, the properties of the bead starting materials packed therein, and so on. For example, bead starting materials with a low degree of expansion may be used in regions requiring strength so as to increase the strength/rigidity of the molded article, while bead starting materials with a high degree of expansion may be used in other regions in order to reduce the weight of the molded article, so as to impart both improved strength and reduced weight to the molded article.
Further, since at least some of the plurality of partitioned molding sections constituting the partitioned mold chambers within the mold are unitary, relative motion of adjacent partitioned molding sections due to mold expansion or contraction is prevented, improving the precision of molding.
Partitioning members include fixed partitioning members provided in fixed fashion to the mold, and moveable partitioning members retractably provided to the mold. In-mold foam molding apparatuses can be broadly classified into three types: those equipped with both fixed partitioning members and moveable partitioning members; those equipped with moveable partitioning members only; and those equipped with fixed partitioning members only.
First Type:
In-mold foam molding apparatus equipped with both fixed partitioning members and moveable partitioning members.
In this type of in-mold foam molding apparatus, the mold cavity is dividable into a plurality of partitioned mold chambers by means of moveable partitioning members extendable and retractable into and from the mold cavity through the core mold or cavity mold, and fixed partitioning members unitary with the core mold or cavity mold. Partitioned molding segments defined by the partitioned mold chambers within in the mold equipped with moveable partitioning members are unitarily formed at locations corresponding to the fixed partitioning members.
In this in-mold foam molding apparatus, with the mold cavity partitioned into a plurality of partitioned mold chambers by the moveable partitioning members and fixed partitioning members, bead starting materials having different properties can be packed into adjacent partitioned mold chambers to achieve the effects described earlier. During the process of molding a molded article, once the mold cavity has been filled with bead starting materials, the bead starting materials are heated and fused with steam. With this in-mold foam molding apparatus, since the moveable partitioning members are retractably provided within the mold cavity, by retracting the moveable partitioning members after the mold cavity has been filled with bead starting materials and prior to fusing together the bead starting materials with steam, it is possible to achieve sufficient bonding among bead starting materials at the interfaces of bead starting materials having different properties, and to thereby assure adequate molding strength at these interfaces.
Further, since partitioned molding segments defined by the partitioned mold chambers within the mold equipped with moveable partitioning members are unitarily formed at locations corresponding to the fixed partitioning members, relative motion of adjacent partitioned molding sections occurring with mold expansion or contraction is prevented, thereby preventing change in width in passage orifice apertures. The retractable configuration of the moveable partitioning members allows a simple linear configuration to be used for the passage orifices formed in the mold, and the passage orifices can be made shorter, preventing expansion/contraction of passage orifice aperture width or deformation of the passage orifices due to mold expansion or contraction, and assuring smooth movement of the moveable partitioning members.
The fixed partitioning member configuration is arbitrary and may take the form of a rod or wall, or a comb configuration provided with a plurality of teeth extending in cantilever fashion in the mold parting direction, arranged at intervals small enough to prevent passage of at least one variety of bead starting materials packed into adjacent partitioned mold chambers. The fixed partitioning members may be arranged at arbitrary locations provided that the locations thereof are aligned with the two ends or medial portion of the boundary of adjacent partitioned mold chambers. Where this boundary is square, fixed partitioning members of rod configuration may be arranged in corner portions of the boundary so as to provide linear configurations for passage orifices, and a fixed partitioning member of wall or comb configuration may be situated along at least one side of the boundary. Where the boundary is linear, fixed partitioning members may be arranged at the two ends or medial portion thereof.
Second Type:
In-mold foam molding apparatus equipped with moveable partitioning members only.
This in-mold foam molding apparatus comprises moveable partitioning members extendable and retractable into and from the mold cavity, for partitioning the mold cavity into a plurality of partitioned mold chambers. The plurality of moveable partitioning members which define the partitioned mold chambers are divided into two sets: first moveable partitioning members arranged on the core mold and second moveable partitioning members arranged on the cavity mold. The plurality of partitioned molding sections of the core mold which constitute the partitioned mold chambers are unitarily formed at locations corresponding to the second moveable partitioning members provided to the cavity mold, and the plurality of partitioned molding sections of the cavity mold which constitute the partitioned mold chambers are unitarily formed at locations corresponding to the first moveable partitioning members provided to the core mold.
As with the in-mold foam molding apparatus of the first type, with this in-mold foam molding apparatus, the functionality and quality of molded articles can be improved through appropriate selection of partitioned mold chamber molding location and size, the properties of the bead starting materials packed therein, and so on. By retracting the moveable partitioning members prior to fusing together the bead starting materials with steam, it is possible to achieve sufficient bonding among bead starting materials at the interfaces of bead starting materials having different properties, and to thereby assure adequate molding strength at these interfaces.
In this in-mold foam molding apparatus, the mold cavity is partitioned into a plurality of partitioned mold chambers by at least two first and second moveable partitioning members. Since first partitioning members are arranged on the core mold and second partitioning members are arranged on the cavity mold, a plurality of partitioned molding sections of the core mold are unitarily formed at locations corresponding to the second partitioning members provided to the cavity mold, and a plurality of partitioned molding sections of the cavity mold are unitarily formed at locations corresponding to the first partitioning members provided to the core mold.
As a result, relative motion of adjacent partitioned molding sections occurring with mold expansion or contraction is prevented, thereby preventing change in width in passage orifice apertures provided to the core mold and cavity mold for the purpose of guiding the moveable partitioning members during retraction thereof. A simple linear configuration can be adopted for the passage orifices, preventing expansion/contraction of passage orifice aperture width or deformation of passage orifices due to mold expansion or contraction, and assuring smooth movement of the moveable partitioning members. Additionally, with this in-mold foam molding apparatus, since the partitioned mold chambers are partitioned by means of moveable partitioning members exclusively, the molded article is devoid of through-holes at locations corresponding to fixed partitioning members, as occurs when fixed partitioning members are used, thereby avoiding loss of strength or diminished appearance of the molded article.
In preferred practice, a core mold or cavity mold provided with moveable partitioning members will be further provided with passage orifices for the purpose of passage of the moveable partitioning members, and projecting portions that project into the mold cavity will be formed along the passage orifice, with the passage orifice aperture leading into the mold cavity being situated medially in the cross direction of these projecting portions. Flash projecting outward from a visible surface of a molded article is produced when bead starting materials infiltrate into the passage orifice apertures, which communicate with the mold cavity when the moveable partitioning members are retracted. With the present in-mold foam molding apparatus, however, projecting portions that project into the mold cavity are formed along the passage orifice, with the passage orifice aperture leading into the mold cavity being situated medially in the cross direction of the projecting portions, these projecting portions forming a recess in the molded article, whereby the flash projects from the back end of the recess. Thus, by selecting the depth of the recess so as to be deeper than the height of the flash, it is possible to produce a molded article that, while having flash, is devoid of flash projecting outwardly from visible surfaces of the molded article. This obviates the need for subsequent flash removal processes, allows the molded article to be attached tightly to the mounting face of a mounting object at the proper location with substantially no gap therebetween, and allows the molded article to be sheathed tightly by a cover member tightly attached thereto with substantially no gap therebetween.
The flash countermeasure described above may be implemented in in-mold foam molding apparatuses of other configurations having moveable partitioning members. The in-mold foam molding apparatus herein provided with this flash countermeasure is provided with moveable partitioning members for partitioning the mold cavity into a plurality of partitioned mold chambers, these members being extendable into and retractable from the mold cavity through passage orifices provided to either the core mold or the cavity mold or both, with projecting portions that project into the mold cavity being formed along the passage orifices provided to the mold(s), and the passage orifice leading into the mold cavity being situated medially in the cross direction of these projecting portions.
With this in-mold foam molding apparatus, with the mold cavity partitioned into a plurality of partitioned mold chambers by partitioning members, adjacent partitioned mold chambers can be filled with bead starting materials having different properties, allowing the functionality and quality of molded articles to be improved through appropriate selection of partitioned mold chamber molding location and size, the properties of the bead starting materials packed therein, and so on. For example, bead starting materials with a low degree of expansion may be used in regions requiring strength so as to increase the strength/rigidity of the molded article, while bead starting materials with a high degree of expansion may be used in other regions in order to reduce the weight of the molded article, so as to impart both improved strength and reduced weight to the molded article.
During the process of molding a molded article, once the mold cavity has been filled with bead starting materials, the bead starting materials are heated and fused with steam. With this in-mold foam molding apparatus, since the moveable partitioning members are retractably provided within the mold cavity, by retracting the moveable partitioning members after the mold cavity has been filled with bead starting materials and prior to fusing together the bead starting materials with steam, it is possible to achieve sufficient bonding among bead starting materials at the interfaces of bead starting materials having different properties, and to thereby assure adequate molding strength at these interfaces.
Further, as noted, flash projecting outward from a visible surface of a molded article is produced when bead starting materials infiltrate into the passage orifice apertures, which communicate with the mold cavity when the moveable partitioning members are retracted. With the present in-mold foam molding apparatus, however, projecting portions that project into the mold cavity are formed along the passage orifices provided to the mold, with the passage orifice opening into the mold cavity being situated medially in the cross direction of the projecting portions, whereby, as described previously, flash projecting outwardly from visible surfaces of the molded article can be eliminated.
In preferred practice, the width of the passage orifice aperture will be smaller than the diameter of the bead starting materials. Where passage orifice aperture width is greater than the diameter of the bead starting materials, bead starting materials will tend to infiltrate into the passage orifices, resulting in a large amount of flash; accordingly, in order to minimize infiltration of bead starting materials into the passage orifices, the width of the passage orifice aperture will be smaller than the diameter of the bead starting materials.
Further, in preferred practice, the height of the projecting portions will be greater than the height of flash formed by the passage orifice. Since flash narrows towards its distal edge, even if the distal edge portion thereof should protrude out to some extent from a visible surface of a molded article, this distal edge portion will deform and be forced into the recess when the molded article is sheathed with a cover member, for example, so that no gap is formed between the molded article and the cover member. However, where the height of the projecting portions is greater than the height of the flash formed by the passage orifice, it can be assured that flash formed by the passage orifice will not project outward from a visible surface of the molded article.
Another possible countermeasure for flash is to design the length of the moveable partitioning members such that, with the moveable partitioning members retracted, the front edge of the moveable partitioning member is coplanar with, or projects beyond the inside face of mold into the mold cavity of the mold provided with the moveable partitioning members.
With this in-mold foam molding apparatus, as with the preceding in-mold foam molding apparatus, the functionality and quality of molded articles to be improved through appropriate selection of partitioned mold chamber molding location and size, the properties of the bead starting materials packed therein, and so on; and by retracting the partitioning members prior to fusing together the bead starting materials, it is possible to achieve sufficient bonding among bead starting materials at the interfaces of bead starting materials having different properties, and to thereby assure adequate molding strength at these interfaces.
Further, since the moveable partitioning members are of length such that, when retracted, the front edge of the moveable partitioning member is coplanar with, or projects beyond the inside face of mold into the mold cavity of the mold provided with the moveable partitioning members, passage orifices are prevented from communicating with the mold cavity when the moveable partitioning members are retracted, thus preventing bead starting materials from filling the passage orifices, thus preventing flash. Thus, when the molded article is sheathed with a cover member or the like, the absence of flash allows the cover member to be secured attached about the outside of the molded article.
As noted, moveable partitioning members may be of comb configuration. Where partitioning members of comb form are moveable, it is necessary to provide the mold with a multitude of passage orifices for passage of the teeth, which makes fabrication of the mold rather complicated. Accordingly, a plate configuration is preferred.
Moveable partitioning members may alternatively consist of plate members having formed therein through-holes or slits of a size that does not allow the bead starting materials to pass. In this case, adjacent partitioned mold chambers communicate via the through-holes or slits provided to the moveable partitioning members, preventing the moveable partitioning members from hindering expulsion of the air used to fill the mold with bead starting materials.
Third type:
In-mold foam molding apparatus equipped with fixed partitioning members only.
In this in-mold foam molding apparatus, fixed partitioning members attached in fixed fashion to the core mold, cavity mold, or both, partition the mold cavity into a plurality of partitioned mold chambers, each partitioned mold chamber being provided with a filling device whereby adjacent partitioned mold chambers can be filled with bead starting materials having different properties. The fixed partitioning members are of comb configuration provided with a plurality of teeth extending in cantilever fashion in the mold parting direction, arranged at intervals small enough to prevent passage of at least one variety of bead starting materials packed into adjacent partitioned mold chambers.
In this in-mold foam molding apparatus, with the mold cavity being partitioned into a plurality of partitioned mold chambers by the fixed partitioning members, adjacent partitioned mold chambers can be filled with bead starting materials having different properties, allowing the functionality and quality of molded articles to be improved through appropriate selection of partitioned mold chamber molding location and size, the properties of the bead starting materials packed therein, and so on. For example, bead starting materials with a low degree of expansion may be used in regions requiring strength so as to increase the strength/rigidity of the molded article, while bead starting materials with a high degree of expansion may be used in other regions in order to reduce the weight of the molded article, so as to impart both improved strength and reduced weight to the molded article.
While molded articles molded by means of this in-mold foam molding apparatus will have formed therein through-holes or wells at locations corresponding to the teeth of the fixed partitioning members, the fixed provision of fixed partitioning members has the following advantages.
(1) The need for a drive system to drive the partitioning members is obviated, allowing the design of the in-mold foam molding apparatus to be appreciably simplified, reducing the costs of fabricating the in-mold foam molding apparatus.
(2) Since the fixed partitioning member attachment locations can be changed, the partitioned zones within the mold cavity can be easily changed to accommodate modifications in molding design and the like.
(3) Since bead starting materials of different properties filling adjacent partitioned mold chambers fuse to a sufficient extent through the spaces between the teeth, adequate bond strength between molded portions consisting of bead starting materials of different properties in a molded article is assured.
(4) Since the need to provide the mold with passage orifices for passage of partitioning members is obviated, the problem of flash formation due to infiltration of bead starting materials into the passage orifices or infiltration between a passage orifice and the partitioning members situated therein is prevented. Localized reductions in mold strength due to the passage orifices is prevented, and molding precision may be improved.
Suitable teeth are rod-like elements 1 to 10 mm in diameter. As noted, with this in-mold foam molding apparatus, through-holes or wells are formed in the molded article by the teeth, so where tooth diameter exceeds 10 mm, through-holes or wells of appreciable size will form, reducing the strength of the molded article and adversely affecting its appearance. Where tooth diameter is smaller than 1 mm, the teeth will not have adequate strength and may break or deform.
The gaps between the teeth should be equal to 30-90% of the diameter of the bead starting materials whose passage is to be prevented. If gaps between adjacent teeth are too small, adequate fusion of bead starting materials contained in adjacent partitioned mold chambers situated to either side of the teeth cannot be assured, resulting in diminished strength at the interface. Bead starting materials consisting of polyolefin resins are softer than bead starting materials consisting of polystyrene resins, and if the gaps between adjacent teeth are too large the bead starting materials may pass between the teeth of the partitioning member and enter the adjacent partitioned mold chamber.
In preferred practice, the teeth will be fabricated of an elastically deformable material. That is, in order to prevent deformation of the teeth due to filling pressure, expansion pressure, or the like, it is ordinarily desirable to make the sectional area thereof rather large in order to increase rigidity, but this has the result of large through-holes or wells being formed in the molded article, causing diminished appearance and lowered strength in the molded article. By fabricating the teeth from an elastically deformable material, the teeth can be designed to recover to their original shape after undergoing deformation of the teeth due to filling pressure, expansion pressure, or the like, thus preventing molding defects due to plastic deformation of the teeth, while at the same time minimizing the sectional area of each tooth, whereby diminished appearance and lowered strength in molded articles may be held in check. The tooth configuration described here may be employed in in-mold foam molding apparatuses of the first type where toothed members are employed as the fixed partitioning members.
In preferred practice, the teeth will be arranged in a rectangular wave, triangular wave, or sine wave arrangement. With this design, boundaries of adjacent molded sections formed in the molded article by adjacent partitioned mold chambers will be imparted with a rectangular wave, triangular wave, or sine wave configuration. This maximizes the area of contact between adjacent molded sections, improving bond strength at the interfaces in the molded article.
To improve release of the molded article, fixed partitioning members will preferably be fixed to a mold having an ejector pin. Depending on mold configuration, a molded article may remain on the mold devoid of an ejector pin when the molds are parted, resulting in failure to release. With the present in-mold foam molding apparatus, however, the molded article is held engaged by the teeth when the molds are parted, and thus remains on the mold provided with the fixed partitioning members. Thus, release failure in the nature of that described above may be effectively prevented by fixing the fixed partitioning members to a mold having an ejector pin.
In preferred practice, fixed partitioning members will be composed of first fixed partitioning members fixed to a mold having an ejector pin and second fixed partitioning members fixed to the mold devoid of an ejector pin. With this arrangement, when the molds are parted to release the molded article, as the teeth of the first fixed partitioning members and the teeth of the second fixed partitioning members pull apart from each other, the molded article disengages from the second fixed partitioning members and is held skewered on the teeth of the first fixed partitioning members, whereby the molded article is released from the mold having the second fixed partitioning members affixed thereto and remains on the mold having the first fixed partitioning members affixed thereto. Thus, when the molded article is released through the agency of the ejector pin, as regards the teeth, it is sufficient simply to extract the molded article from the teeth of the first fixed partitioning members, thereby providing markedly easier release than is the case where the molded article must be extracted from both sets of teeth. Further, when the molds are parted to release the molded article, as the teeth of the first and second fixed partitioning members pull apart from each other, areas of adhesion between the molded article and the teeth of the first fixed partitioning member on which the molded article remains are separated to a certain extent, thereby facilitating release of the molded article by the ejector pin.
Where the fixed partitioning members are composed of first fixed partitioning members fixed to a mold having an ejector pin and second fixed partitioning members fixed to the mold devoid of an ejector pin, in preferred practice the teeth of the first fixed partitioning members and the teeth of the second fixed partitioning members will be arranged in alternating fashion, or the number of teeth of the first fixed partitioning members fixed to the mold having an ejector pin will be greater than the number of teeth of the second fixed partitioning members fixed to the mold devoid of an ejector pin. The former configuration affords good balance when the teeth of the first fixed partitioning members and the teeth of the second fixed partitioning members are pulled apart from each other as the molds are parted, preventing the molded article from being subjected to unnecessary force. The latter configuration assures that the molded article will be held retained on the mold having an ejector pin.
In preferred practice, the gaps between the teeth of the first fixed partitioning members and the second fixed partitioning members will be such that at least one of the bead starting materials being used cannot pass therethrough. By doing so, passage of bead starting materials between adjacent partitioned mold chambers can be prevented, even without extending the distal ends of the teeth of the first fixed partitioning members and the second fixed partitioning members as far as the inside wall of the other mold, simply by overlapping by a certain extent the distal ends of the teeth of the two sets of fixed partitioning members in the axial direction of the teeth. It is therefore possible to make the teeth of the two sets of fixed partitioning members shorter, thereby improving release of the molded article and minimizing the action of bending moment on the teeth, whereby teeth of smaller diameter can be used so that the diameter of the wells formed in the molded article by the teeth is smaller. Since tooth length may be set roughly, it can readily be modified in accordance with a change in the shape of the molded article or the like, and in cases where a crack is maintained between the two molds as they are filled with the bead starting materials (such in cracked filling), by designing the lap of the teeth of the two sets of fixed partitioning members to exceed the width of the crack, adjacent partitioned mold chambers can be kept partitioned.
While tooth configuration may be selected arbitrarily, by providing to the distal end or medial portion of fixed partitioning members fixed to the ejector pin-equipped mold a release-resistance increasing portion for the purpose of increasing resistance to release of the molded article from the teeth, it is possible to assure that when the molds are parted, the molded article remains on the mold having an ejector pin.
The first in-mold foam molding method which pertains to the invention employs an in-mold foam molding apparatus comprising: a core mold and a cavity mold that are devoid of air orifices (such as core vents and core vent holes) in those molding sections used for molding prominent areas of the outside face of a molded article; and moveable partitioning members that partition the mold cavity so as to prevent passage of the bead starting materials, these moveable partitioning members being retractable from the mold cavity by means of drive means. With the mold cavity partitioned into a plurality of partitioned mold chambers by the moveable partitioning members, bead starting materials of different properties are packed into adjacent partitioned mold chambers, and when these are filled with bead starting materials, the moveable partitioning members are retracted while supplying steam to the bead starting materials to fuse them together.
In this molding method, the in-mold foam molding apparatus used comprises a core mold and a cavity mold that are devoid of air orifices (such as core vents and core vent holes), whereby marks produced on the molded article surface by air orifices are situated in obscured areas of the molded article surface, thereby improving the attractiveness of the molded article surface.
Further, in this molding method, air orifices may be dispensed with entirely or substantially entirely, and the flows of service fluid to the rear chamber of the core mold, the rear chamber of the cavity mold, and the mold cavity may be controlled separately. For example, where heating conditions in these spaces are manipulated independently through control of a steam service fluid, the surface qualities of the bead starting material portions contacting the core mold and cavity mold within the filled mold cavity can be controlled through the agency of steam delivered to the two chambers, while heating, expansion, and fusion of the bead starting materials filling the mold cavity can be controlled through the agency of steam delivered to the mold cavity, whereby fusion of the bead starting materials can be controlled independently of surface qualities. In this way, fusion in a molded article can be held to a lower level, shortening the molding cycle time and producing a molded article with an attractive surface, thereby achieving both good throughput and high product value.
In preferred practice, the bead starting materials will comprise polyolefin resin bead starting materials in order to assure that the bead starting materials are adequately packed into the mold cavity. Specifically, in terms of achieving accurate control of the supply of service fluid to the two chambers and to the mold cavity, it is ideal in the present molding method for the molds to be devoid of air orifices; however, this arrangement results in a susceptibility to turbulence in the air used for filling the bead starting materials, creating a concern that packing of bead starting materials may suffer. Bead starting materials consisting of polyolefin resins, however, are soft materials and are moreover highly gas permeable, so for a given expansion factor, polyolefin resin bead starting materials experience appreciably more particle shape deformation, contributing to improved packing, so that an overall decline in packing is effectively prevented.
Further, with this molding method, with the mold cavity partitioned into a plurality of partitioned mold chambers by means of moveable partitioning members, adjacent partitioned mold chambers may be filled with bead starting materials of different properties, allowing each partitioned mold chamber to be filled with bead starting materials of different properties. For example, bead starting materials with a low degree of expansion may be used in regions requiring strength so as to increase the strength/rigidity of the molded article, while bead starting materials with a high degree of expansion may be used in other regions in order to reduce the weight of the molded article, so as to impart both improved strength and reduced weight to the molded article. Since the moveable partitioning members are retractable from the mold cavity by drive means, once the mold cavity has been filled with the bead starting materials, the partitioning members can be withdrawn to allow the bead starting materials to be heated and fused with steam, thereby affording adequate bonding even at the interfaces between bead starting materials of different properties. The smooth transition between the two types of bead starting materials prevents the appearance of the molded article from suffering.
The second in-mold foam molding method which pertains to the invention employs an in-mold foam molding apparatus comprising: a core mold and a cavity mold that are devoid of air orifices (such as core vents and core vent holes) in those molding sections used for molding prominent areas of the outside face of a molded article; and fixed partitioning members of comb configuration having a plurality of teeth for partitioning the mold cavity so as to prevent passage of the bead starting materials, these fixed partitioning members being fixed to the core mold or cavity mold with the teeth thereof arranged in the direction of mold parting. Bead starting materials of different properties are packed into adjacent partitioned mold chambers defined within the mold cavity by the fixed partitioning members, and steam is then supplied to the bead starting materials to heat and fuse them together.
This molding method affords the same advantages as the first molding method described previously. In distinction from the first molding method, however, fixed partitioning members are fixedly provided to the core mold or cavity mold, so that the bead starting materials must be heated and fused with the fixed partitioning members in situ within the mold cavity, and as a result through-holes are produced in the molded article at locations corresponding to those of the teeth. However, the need for a drive mechanism for driving the partitioning members is obviated, as is the need for a sealing structure between the mold and the partitioning members, so the design of the in-mold foam molding apparatus can be greatly simplified, significantly reducing the costs entailed in fabrication thereof. Further, the partitioned areas in the mold cavity can be readily modified by changing the locations at which the fixed partitioning members are attached, allowing for easy adaptation to changes in molding design and the like.
The air orifices in the core mold and cavity mold may be dispensed with entirely or substantially entirely. This affords precision control of heating conditions for the three spaces, namely, the rear chamber of the core mold, the rear chamber of the cavity mold, and the mold cavity, and affords an attractive molding surface free from marks produced by air orifices. Further, the lack of air orifices prevents cooling water sprayed into the two chambers during cooling from contacting the molded article, thus preventing a rise in the water contact of the molded article due to contact with cooling water. Since cooling water does not come into direct contact with the molded article, sanitary molded articles can be obtained.
The third in-mold foam molding method which pertains to the invention employs the in-mold foam molding apparatus recited in any of claims 1 to 13, wherein with the mold cavity partitioned into a plurality of partitioned mold chambers by moveable partitioning members extended therein, bead starting materials are packed into the mold cavity such that at least adjacent partitioned mold chambers are filled with bead starting materials of different properties, and when these are filled with bead starting materials, the moveable partitioning members are retracted until the bead starting materials are fused together by means of steam supplied thereto.
This molding method employs an in-mold foam molding apparatus of the first or second type, wherein with the mold cavity partitioned into a plurality of partitioned mold chambers by means of moveable partitioning members and fixed partitioning members, and bead starting materials are packed into the mold cavity such that at least adjacent partitioned mold chambers are filled with bead starting materials of different properties, whereby functionality and quality of molded articles may be improved through appropriate selection of partitioned mold chamber molding location and size, the properties of the bead starting materials packed therein, and so on. For example, bead starting materials with a low degree of expansion may be used in regions requiring strength so as to increase the strength/rigidity of the molded article, while bead starting materials with a high degree of expansion may be used in other regions in order to reduce the weight of the molded article, so as to impart both improved strength and reduced weight to the molded article.
Further, after filling with the bead starting materials, the moveable partitioning members are retracted until the bead starting materials are fused together by means of steam supplied thereto, thereby affording adequate bonding at interfaces between bead starting materials of different qualities and assuring adequate molding strength at these interfaces.
Further, the use of an in-mold foam molding apparatus of the first or second type wherein adjacent partitioned mold chambers are unitary prevents relative motion of adjacent partitioned molding sections due to mold expansion or contraction and prevents changes in the width of the passage orifices. The configuration of the passage orifices provided to the mold for passage of the moveable partitioning members can be simplified, for example, to a linear configuration, and expansion/contraction of passage orifice aperture width or deformation of passage orifices due to mold expansion or contraction can be prevented, assuring smooth movement of the moveable partitioning members.
In preferred practice, according to this third molding method, the mold cavity will first be filled with bead starting materials, the moveable partitioning members will be retracted, and the bead starting materials will then be heated and fused. The timing at which the moveable partitioning members are retracted may be selected arbitrarily provided that retraction occurs at some point after packing the bead starting materials and before the bead starting materials become fused together by steam supplied thereto. In actual practice, the timing at which the bead starting materials are fused together by the steam will differ depending on the size of the molded article, and will also vary by area within the molding cavity, with steam temperature, and other factors, making it difficult to achieve specific timing. Accordingly, in preferred practice the moveable partitioning members will be retracted after packing the bead starting materials and before delivering steam to the mold cavity.
The fourth in-mold foam molding method which pertains to the invention employs the in-mold foam molding apparatus recited in any of claims 14 to 24, and additionally employs as the bead starting materials bead starting materials that cannot pass through the teeth. With the core mold and cavity mold shut so that the mold cavity is partitioned into a plurality of partitioned mold chambers by fixed partitioning members, these bead starting materials fill the partitioned mold chambers in such a way that at least adjacent partitioned mold chambers are filled with bead starting materials of different properties.
Since this molding method employs an in-mold foam molding apparatus of the third type, the advantages thereof are analogous to those described earlier. Additionally, since the bead starting materials are of a size that does not allow passage through the teeth of the fixed partitioning members, the plurality of partitioned mold chambers can be filled with bead starting materials of different properties, and bead starting materials can be packed in without prolonging the time needed to pack in the bead starting materials.
The fifth in-mold foam molding method which pertains to the invention employs the in-mold foam molding apparatus recited in any of claims 14 to 24, and additionally employs as the bead starting materials a first bead starting material that cannot pass through the teeth and a second bead starting material that can pass through the teeth. With the core mold and cavity mold shut so that the mold cavity is partitioned into a plurality of partitioned mold chambers by fixed partitioning members, the first bead starting material is packed in, followed by the second bead starting material, packing the bead starting materials into the partitioned mold chambers in such a way that at least adjacent partitioned mold chambers are filled with bead starting materials of different properties.
Since this molding method employs an in-mold foam molding apparatus of the third type, the advantages thereof are analogous to those described earlier. Additionally, since a first bead starting material that cannot pass through the teeth is packed first, followed by a second bead starting material that can pass through the teeth, while the filling process is more time consuming, improved bond strength between the first beads and the second beads is afforded, since a portion of the second beads pass through the teeth and migrate to adjacent partitioned mold chambers.
Adjacent partitioned mold chambers partitioned by means of partitioning members are filled with bead starting materials of different properties, which may conceivably be bead starting materials having different degrees of expansion. For example, bead starting materials with a low degree of expansion may be used in regions requiring strength so as to increase the strength/rigidity of the molded article, while bead starting materials with a high degree of expansion may be used in other regions in order to reduce the weight of the molded article, so as to impart both improved strength and reduced weight to the molded article.
The first in-mold foam molded article which pertains to the invention has formed thereon a recess extending along an exterior face of an interface of molded portions molded from bead starting materials of different properties, with flash being formed on the bottom face of the recess so as to not project outward from visible surfaces of the molded article.
In this molded article, flash does not project outward from visible surfaces of the molded article, obviating the need for a finishing process to remove flash or the like, and allowing the molded article to be attached tightly to the mounting face of a mounting object at the proper location with substantially no gap therebetween and allowing the molded article to be sheathed tightly by a cover member tightly attached thereto with substantially no gap therebetween. Molded articles of this kind can be fabricated by means of the in-mold foam molding apparatus described hereinabove provided with projecting portions situated along the passage orifice.
The second in-mold foam molded article which pertains to the invention has a plurality of molded portions molded from bead starting materials of different properties, and has formed therein a plurality of through-holes or wells situated at predetermined intervals along the interfaces of the molded portions and extending in the direction of mold parting.
Molded articles of this kind are molded using an in-mold foam molding apparatus provided with teeth, the through-holes or wells being situated at locations corresponding to those of the teeth. Thus, the design of the in-mold foam molding apparatus can be simplified, and the need to provide the mold with passage orifices for extending and retracting the partitioning members vis-à-vis the mold cavity in the manner described earlier is obviated, whereby formation of flash projecting from visible surfaces of the molded article by passage orifices is eliminated.
In preferred practice, those exterior portions of an interface that are devoid of through-holes or wells will have formed therein a recess extending along the interface so that flash formed on the bottom of the recess does not project out from visible surfaces of the molded article. In molded articles of this kind, flash does not project out from visible surfaces of the molded article, thereby obviating the need for a finishing process to remove flash or the like, and allowing the molded article to be attached tightly to the mounting face of a mounting object at the proper location with substantially no gap therebetween and allowing the molded article to be sheathed tightly by a cover member tightly attached thereto with substantially no gap therebetween.
In preferred practice, interfaces between molded sections will have a rectangular wave, triangular wave, or sine wave configuration. This maximizes the area of contact between adjacent molded sections, improving bond strength and improving the strength of the molded article.
A specific example of an in-mold foam molded article is a core for an automobile bumper. Automobile bumper cores of this kind must be capable of efficiently absorbing shock occurring during frontal impact of the automobile (frontal impact), shock occurring with offset impact, and shock occurring with frontal impact on the diagonal (diagonal impact). In addition, in order to hold down vehicle weight, the weight of the core must be as light as possible. In the automobile bumper core which pertains to the present invention, portions of the core susceptible to localized impact stress during automobile frontal collisions of various kinds are composed of low-expansion portions consisting of a bead starting material having a low degree of expansion, while other portions are composed of high-expansion portions consisting of a bead starting material having a high degree of expansion, thereby minimizing core weight while providing effective absorption of energy of impact in the case of offset impact or diagonal impact.